This invention relates to the fastening of a leaf spring of composite material, more particularly applicable to heavy vehicles.
Leaf springs of composite material can be obtained by molding or pultrusion. In this case, there is preferably used a thermosetting resin of the polyester or epoxy type including a catalyst that can be activated with heat, and reinforced with unidirectional elements such as wires, glass fibers or strips. Because of this, the products obtained exhibit an anisotropy of their mechanical strength, which very appreciably differentiates them from steel spring leaves; consequently, the usual techniques for fastening steel springs are not transferable to leaf springs of composite material.
Fastenings for composite material leaf springs, as applied on the axle or the axle assembly of a motor vehicle, are known. For example, it has been known to use a bolted-connection of the leaf of synthetic material to the axle assembly, which exhibits the main drawback of weakening the leaf at the opening for the passage of the bolt.
The fastening can also be assured by unregulated clamping of a flange placed directly on the leaf of the spring, which can lead to crushing of the composite material, whose strength in the direction perpendicular to the reinforcement fibers is weak.
A limited intensity clamping of the leaf could also be performed by inserting a rubber element between the clamping flange and the leaf. However, the adherence between the rubber element and the leaf which is intended to take up longitudinal forces particularly when starting and braking the vehicle, while acceptable for an automobile, is insufficient for heavy weight vehicles.